This invention relates to geared rotary actuators for aircraft lift control surfaces.
It is known, for example from PCT Application W086/00968 that a rotary actuator for aircraft lift control surfaces may comprise a plurality of axially aligned compound epicyclic gear trains which are coupled to a common input shaft, each of the gear trains having one or more first output elements coupled to an aircraft wing and one or more second output elements coupled to the control surface.
The present invention provides an actuator comprising an input shaft, at least two substantially axially aligned gear trains, each gear train having a sun input gear drivingly connected to said input shaft, a plurality of compound planet gears, each having a first pinion and two second pinions, said pinions being secured together for rotation in unison, said first pinion meshing with said sun input gear and with a first output ring gear, and second output ring gears drivingly coupled for rotation by respective ones of said second pinions.
When an aircraft lift control surface is deployed, aerodynamic forces urge it to flex in a direction opposite to that of the wing. This flexure imposes varying loads and stiffness distribution on the actuator over its length. Since the gear trains are driven by a common input shaft, each of the gear trains attempts to drive its first and second output ring gears at an identical relative speed, irrespective of variations in load and stiffness. The forces resulting from these variations impose additional loads within the actuator and tend to increase torsion on the elements of the gear trains. In one of its aspects the invention has as an object to balance the torque loads between the gear trains.